A Spindt-type electrode and a carbon nanotube electrode (CNT) have been known as conventional electron emitting elements. Applications of such conventional electron emitting elements to, for example, the field of Field Emission Display (FED) have been studied. Such electron emitting elements are caused to emit electrons by tunnel effect resulting from formation of an intense electric field of approximately 1 GV/m that is produced by application of a voltage to a pointed section.
However, each of these two types of the electron emitting elements has an intense electric field in the vicinity of a surface of an electron emitting section. Accordingly, emitted electrons obtain a large amount of energy due to the electric field. This makes it easy to ionize gas molecules. However, cations generated in the ionization of the gas molecules are accelerated in a direction of a surface of the element due to the intense electric field and collide with the surface. This causes a problem of breakdown of the element due to sputtering.
Further, ozone is generated before ions are generated, because oxygen in the atmosphere has dissociation energy that is lower than ionization energy. Ozone is harmful to human bodies, and oxidizes various substances because of its strong oxidizing power. This causes a problem in that members around the element are damaged. In order to prevent this problem, the members used around the electron emitting element are limited to members that have high resistance to ozone.
Meanwhile, an MIM (Metal Insulator Metal) type and an MIS (Metal Insulator Semiconductor) type have been known as other types of electron emitting elements. These electron emitting elements are surface-emission-type electron emitting elements which accelerate electrons by utilizing quantum size effect and an intense electric field in the element so that electrons are emitted from a flat surface of the element. These electron emitting elements do not require an intense electric field outside the elements, because the electrons which are accelerated in respective electron acceleration layers inside the elements are emitted to the outside. Therefore, each of the MIM type and the MIS type electron emitting elements can overcome such problems that (i) the element is broken down by the sputtering which occurs due to ionization of gas molecules and (ii) ozone is generated, in the Spindt-type, CNT type, and BN type electron emitting elements.
Further, Patent Literature 1, made by the inventors of the present invention, discloses an electron emitting element including: an electrode substrate; a thin-film electrode; and an electron acceleration layer sandwiched between the electrode substrate and the thin-film electrode, which electron acceleration layer contains conductive fine particles and insulating fine particles. By application of a potential difference between the substrate electrode and the thin-film electrode, the electron emitting element emits electrons from the thin-film electrode.
The electron emitting element disclosed in Patent Literature 1 employs, as the electron acceleration layer, an insulating film in which the conductive fine particles, such as metal particles, are dispersed. Such an arrangement makes it possible to control a volt-ampere characteristic of the electron emitting element by adjusting (i) an amount of the conductive fine particles in the insulating film, and/or (ii) a dispersion state of the conductive fine particles in the insulating film. As disclosed in Patent Literature 1, the inventors of the present invention have succeeded in increasing the amount of emitted electrons by appropriately adjusting the amount of the conductive fine particles added to the insulating film, and/or the dispersion state of the conductive fine particles in the insulating film.